Flutterbird is a free, open-source effect plugin for adding pitch and volume fluctuation to incoming audio. It can be used for traditional wow/flutter effects as well as more chaotic, extreme modulation.

Flutterbird has four separate oscillators with adjustable speeds that can be mapped to either pitch or volume.

Excellent, well-designed, intuitive plugin capable of all kinds of detunes, warbles, and flutters, Especially great are the long, slowly evolving pitch bends that can get complex when you start combining waveforms. My top choice in the 2018 KVR developer challenge, outstanding - thank you!.